Magnetic tunnel junction structures and related methods

ABSTRACT

The disclosure is directed to spin-orbit torque MRAM structures and methods. A SOT channel of the SOT-MRAM includes multiple heavy metal layers and one or more dielectric dusting layers each sandwiched between two adjacent heavy metal layers. The dielectric dusting layers each include discrete molecules or discrete molecule clusters of a dielectric material scattered in or adjacent to an interface between two adjacent heavy metal layers.

Magnetoresistive random-access memory (“MRAM”) is a promisingnon-volatile data storage technology. The core of a MRAM storage cell(or “bit”) is a magnetic tunnel junction (“MTJ”) in which a dielectriclayer is sandwiched between a magnetic fixed layer (“reference layer”)and a magnetic free layer (“free layer”) whose magnetization orientationcan be changed. Due to the tunnel magnetoresistance effect, theresistance value between the reference layer and the free layer changeswith the magnetization orientation switch in the free layer. Parallelmagnetizations (“P state”) lead to a lower electric resistance, whereasantiparallel magnetizations (“AP state”) lead to a higher electricresistance. The two states of the resistance values are considered astwo logic states “1” or “0” that are stored in the MRAM cell.

In a spin transfer torque MRAM (“STT-MRAM”) cell, the write current isapplied passing through the entire MTJ, i.e., reference layer, thedielectric layer, and the free layer, which sets the magnetizationorientation of the free layer through the spin transfer torque effect.That is, the write current passes through a same path as the read pathof the MRAM. In a spin-orbit torque MRAM (“SOT-MRAM”) cell, a MTJstructure is positioned on a heavy metal layer with large spin-orbitinteraction. The free layer is in direct contact with the heavy metallayer. Spin torque is induced by the in-plane current injected throughthe heavy metal layer under the spin-orbit coupling effect, whichgenerally include one or more of the Rashba effect or the spin Halleffect (“SHE effect”). The write current does not pass through thevertical MTJ. Instead, the write current passes through the heavy metallayer. The magnetization orientation in the free layer is set throughthe spin-orbit torque effect. More specifically, when a current isinjected in-plane in the heavy metal layer, the spin orbit couplingleads to an orthogonal spin current which creates a spin torque andinducing magnetization reversal in the free layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. In thedrawings, identical reference numbers identify similar elements or actsunless the context indicates otherwise. The sizes and relative positionsof elements in the drawings are not necessarily drawn to scale. In fact,the dimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is an example MRAM cell according to example embodiments of thedisclosure;

FIG. 2 is an top view of an example MTJ structure positioned withrespect to an SOT metal layer according to example embodiments of thedisclosure;

FIG. 3 is an example operation configuration an example write operationto the MRAM cell according to example embodiments of the disclosure;

FIGS. 4A to 4D are example stages of switching a MTJ from P state to APstates according to example embodiments of the disclosure;

FIGS. 5A to 5D are example stages of switching a MTJ from AP state to Pstates according to example embodiments of the disclosure;

FIGS. 6A to 6D are various timing control configurations of switching aMTJ between P state and AP states according to example embodiments ofthe disclosure;

FIG. 7 is an example precession process of a magnetization orientationof a free layer according to example embodiments of the disclosure;

FIG. 8 is another example precession process of a magnetizationorientation of a free layer according to example embodiments of thedisclosure; and

FIG. 9 is an example process of a write operation to an example MRAMcell according to example embodiments of the disclosure.

DETAILED DESCRIPTION

The current techniques in accordance with embodiments described hereinare created based on the observation that in perpendicular spin-orbittorque (“SOT”) MRAM systems, the application of the SOT current tend topull the magnetization orientation of the free layer from a verticalorientation, either AP or P with respect to that of the reference layer,to an in-plane orientation following the shape anisotropy of the freelayer. However, this in-plane magnetization orientation is temporary andis maintained only under the SOT effect. After the SOT current isremoved, the magnetization orientation of the free layer may settle backto a perpendicular orientation randomly in one of the AP or the P state.That is, the SOT effect does not determinatively switch the state of theMTJ, and the perpendicular MTJ has a substantially equal probability ofsettling in a P state or in an AP state after the SOT effect.Conventionally, an external in-plane magnetic field is applieddeterminatively settle the perpendicular magnetization orientation ofthe free layer, together with the SOT effect. However, the externalmagnetic field is detrimental to the device or the circuit and theoperations thereof. A large canting angle between the shape anisotropyof the free layer, e.g., a long-axis of an elliptic free layer, and theSOT current flow direction may also be used to help set theperpendicular magnetization orientation of the free layer. A largecanting angle is usually in the range of 30 degree to 60 degree or 120degree to 150 degree. However, such a large canting angle substantiallyincreases power consumption and/or reduces switching speed.

The disclosed techniques are directed to a new SOT-MRAM structure wherea voltage controlled magnetic anisotropy (“VCMA”) is adopted todeterminatively set the perpendicular magnetization orientation of thefree layer. Specifically, in an embodiment, a VCMA voltage source iscoupled between the reference layer and the free layer of the MTJstructure of the SOT-MRAM. As such, the VCMA voltage source basicallyapplies a VCMA voltage on the tunnel barrier layer of the MTJ structure.In an embodiment, the VCMA voltage is sufficiently large toovercome/eliminate the energy barrier accumulated by the tunnel barrierlayer that prevents the switching between the AP state and the P stateof the MTJ structure. At the same while, the VCMA voltage is not solarge as to break the dielectric barrier of the tunnel barrier layerlike in the STT-MRAM configurations. For this reason, in someembodiment, the tunnel barrier layer may have a larger thickness thancomparable SOT-MRAM devices that does not have the VCMA mechanism.

The VCMA voltage is applied after the SOT current pulls the free layermagnetization into the in-plane shape anisotropy orientation. With theSOT current removed, the VCMA voltage functions to remove the energybarrier accumulated around the tunnel barrier layer of the MTJ. Withoutthe energy barrier, the magnetization orientation of the free layerenters into a precession process and rotate/circles around the shapeanisotropy of the free layer. Removal of the VMCA voltage ends theprocession. With proper timing of removing the VCMA voltage, whichcorresponds to a position of the magnetization orientation at the end ofthe precession process (“precession end position”), the magnetizationorientation of the free layer will settle at one of the AP or P statedeterminatively. Specifically, after the VCMA voltage is removed to endthe precession, the magnetization orientation of the free layer willsettle at a perpendicular orientation adjacent to the precession endposition.

The precession process may be simulated or experimentally studied todetermine the timing to start or to stop applying the VCMA voltage. Inanother embodiment, the precession process may be monitored in real timeto determine a time point to stop the VCMA voltage such that the stateof the MTJ settles deterministically. In an embodiment, an earlysettlement of the MTJ state is preferred to improve the switching speedof the MRAM.

The following disclosure provides many different embodiments, orexamples, for implementing different features of the described subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present description. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various embodiments of thedisclosure. However, one skilled in the art will understand that thedisclosure may be practiced without these specific details. In otherinstances, well-known structures associated with electronic componentsand fabrication techniques have not been described in detail to avoidunnecessarily obscuring the descriptions of the embodiments of thepresent disclosure.

Unless the context requires otherwise, throughout the specification andclaims that follow, the word “comprise” and variations thereof, such as“comprises” and “comprising,” are to be construed in an open, inclusivesense, that is, as “including, but not limited to.”

The use of ordinals such as first, second and third does not necessarilyimply a ranked sense of order, but rather may only distinguish betweenmultiple instances of an act or structure.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

FIG. 1 shows an example MTJ bit cell 100 of a SOT-MRAM device. The bitcell 100 includes a MTJ structure 110 that includes a dielectric layer114 sandwiched between a first ferromagnetic layer 112 and a secondferromagnetic layer 116. The first ferromagnetic layer 112 and thesecond ferromagnetic layer 116 include a same type of perpendicularmagnetic anisotropy. The magnetization of the first ferromagnetic layer112 maintains a fixed orientation or orientation, e.g., in the updirection as shown by a unidirectional arrow 120, perpendicular to asubstrate plane (not shown for simplicity) or a plane which the MTJ 110seats on. The magnetization orientation of the second ferromagneticlayer 116 is switchable in the perpendicular axis, as shown by abi-directional arrow 122. The switchable magnetization orientation ofthe second ferromagnetic layer 116 represents two states thereof withrespect to the magnetization orientation of the first ferromagneticlayer 112, a parallel state “P” or an antiparallel state “AP”. In the“P” state, the magnetization orientation of the second ferromagneticlayer 116 is in the same direction as that of the first ferromagneticlayer 112, here in the down direction. In the “AP” state, themagnetization orientation of the second ferromagnetic layer 116 is in adifferent direction as that of the first ferromagnetic layer 112, herein the up direction. In the description herein, the first ferromagneticlayer 112 is referred to as a “reference layer” and the secondferromagnetic layer 116 is referred to as a “free layer”. The dielectriclayer 114 is a tunnel barrier layer that barriers the tunneling ofcharge carriers between the reference layer 112 and the free layer 116.

A SOT metal layer 130 is positioned adjacent to and in electric couplingwith the free layer 116. In an embodiment, the SOT metal layer 130 is indirect contact with the free layer 116. For example, an upper surface130U of the SOT metal layer 130 is in direct contact with a lowersurface 116L of the free layer 116. In some embodiment, to maximize thespin Hall effect (“SHE”) between the SOT metal layer 130 and the freelayer 116, an interface area 132 between the SOT metal layer 130 and thefree layer 116 substantially fully overlaps the lower surface 116L ofthe free layer 116. That is, the upper surface 130U of the SOT metallayer 130 substantially fully overlap the lower surface 116L of the freelayer 116. In an embodiment, the upper surface 130U is larger than thelower surface 116L in at least some directions.

Due to the tunnel magnetoresistance effect, the resistance value betweenthe reference layer 112 and the free layer 116 changes with themagnetization orientation switch in the free layer 116. The parallelmagnetizations (“P state”) lead to a lower electric resistance acrossthe MTJ 110, whereas the antiparallel magnetizations (“AP state”) leadto a higher electric resistance across the MTJ 110. The two states ofthe resistance values are considered as two logic states “1” or “0” thatare stored in the MRAM bit cell 100. In the description herein, the P orAP state are also used to refer to the magnetization orientation in thefree layer 116 with respect to that of the reference layer 112.

The bit cell 100 includes at least three terminals R, W and S. In a readoperation, a signal from a read control line, e.g., a read Word line140, turns on a read transistor 142 to enable a read current to flowbetween a Bit line and a source line through the MTJ structure 110. Avalue of the read current indicates the resistance value of the MTJ 110,i.e., the logic state stored in the MRAM cell 100. In a write operation,a signal from a write control line, e.g., a first write Word line 150,turns on a first write transistor 152 to enable a write current to passthrough the SOT metal layer 130 to generate a spin-orbit torque (“SOT”)that changes the magnetization orientation of the free layer 116. Themechanisms of the SOT effect include one or more of spin Hall effect(“SHE”) or a Rashba effect. The relative ratios between the SHE and theRashba effect depend on the device structure, fabrication processesand/or material choices. However, the current disclosure is applicableto and is not limited by any of these factors and any resultant ratiosbetween the SHE and Rashba effect. In the description herein, it isassumed that SHE dominates the spin-orbit torque (“SOT”). The terms“SHE” or “SOT” may be used interchangeably in referring to thespin-orbit torque effect.

A voltage source V_(VCMA) 154 is coupled to introduce an electric fieldacross the tunnel barrier layer 114 of the MTJ 110. In an embodiment,the V_(VCMA) 154 is coupled between the reference layer 112 and the freelayer 116. More specifically, in an embodiment, the VCMA voltage 154 iscoupled between the reference layer 112 and the SOT metal layer 130,which is conductive and connected to the free layer 112. In anembodiment, the V_(VCMA) 154 may be coupled between the R terminal andone of the W or S terminal. Other coupling configurations are alsopossible and included in the disclosure. In an embodiment, the V_(VCMA)154 is a unidirectional DC voltage, e.g., always positive or alwaysnegative. For example, the high potential end of the V_(VCMA) 154 iscoupled to the reference layer 112 and the low potential end of theV_(VCMA) 154 is coupled to the free layer 122, e.g., through the SOTmetal layer 130. Because the reference layer 112 and the free layer 116are both conductive, the V_(VCMA) 154 basically applies on to thebarrier layer 114. The application of the V_(VCMA) 154 will reduce orremove the energy barrier accumulated on the two sides of the barrierlayer 114 that hampers a switching between the AP state and the P stateof the MTJ structure 110. The application of the V_(VCMA) 154 iscontrolled by a second write transistor 162. A signal line 160 controlsthe on/off of the second write transistor 162. In an embodiment, thesignal line 160 is a second write line, which works together with thefirst write line 150 in completing the “write” operation. In anembodiment, the signal line 150 and the signal line 160 turn on theswitch 152 and the switch 162 sequentially in a write operation, asfurther described herein. In an embodiment, the signal line 150 and thesignal line 160 are timing control outputs of a same write signal line.Other suitable configurations to implement the timing control of thefirst write transistor 152 or the second write transistor 162 are alsopossible and included in the disclosure.

In some embodiments, a bidirectional current may be applied through theSOT metal layer 130 for P to AP state change and for the AP to P statechange, respectively. For the VCMA voltage 154, a unidirectional DCvoltage, is used for both the P to AP state change and for the AP to Pstate change. The voltage value of the V_(VCMA) 154 may be differentbetween the AP to P state switch and the P to AP state switch becausethe involved energy barriers may be different. In an embodiment, theV_(VCMA) 154 may apply a larger voltage value in the AP to P stateswitch than the P to AP state switch.

In an embodiment, the free layer 116 is one or more of Fe, Co, Ni, FeCo,CoNi, CoFeB, FeB, FePt, FePd or other suitable ferromagnetic material.The reference layer 112 is one or more of Fe, Co, Ni, FeCo, CoNi, CoFeB,FeB, FePt, FePd or other suitable ferromagnetic material. In anembodiment, the reference layer 112 is a synthetic anti-ferromagneticstructure that includes one or more non-magnetic (“NM”) metal layerseach sandwiched between two pinned ferromagnetic (“FM”) layers. In anembodiment, the free layer 116 is a synthetic anti-ferromagneticstructure that includes a non-magnetic metal layer sandwiched betweentwo free ferromagnetic layers. For example, the free layer 116 mayinclude a Ta layer sandwiched between two CoFeB layers. In an example, acomposition of a CoFeB material may be Co₂₀Fe₆₀B₂₀ or other suitablecompositions. The tunnel barrier layer 114 is MgO or other suitableheavy metal materials.

The tunnel barrier layer 114 is MgO, Al₂O₃ or other suitable dielectricmaterials.

The SOT metal layer 130 is a heavy metal layer of Ta, W, Pt, Cu, Au orother suitable metal materials or a combination of such metal materialswith dielectric materials.

In some embodiment, a capping layer (not shown for simplicity), e.g., ofWO₂, NiO, MgO, Al₂O₃, Ta₂O₅, MoO₂, TiO, GdO, Al, Mg, Ta, Ru othersuitable materials are formed over the reference layer 112.

The example structure MTJ 110 is provided as an illustrative example ofa SOT-MRAM cell. Alternative or additional MTJ structures and siliconimplementations are also possible and included in the disclosure. Forexample the SOT-MRAM cell may also include a syntheticanti-ferromagnetic (“AFM”) structure layer adjacent to the referencelayer 112 to pin the magnetization orientation of the reference layer112. The synthetic AFM structure may include one or more of bufferlayers of Ta, Ru or other suitable materials, one or more ferromagnetic(“FM”) layers of Co, Fe or other FM materials, one or moreferromagnetic/non-ferromagnetic FM/NM multilayers of Co/Pt, Co/Pd orother combinations of FM/NM materials, or other layers in a syntheticAFM structure. The antiferromagnetic layer and (or ferromagnetic biasinglayer) functions to pin the magnetization orientation of the referencelayer 112. A bottom electrode may be formed adjacent to the SOT metallayer 130 and a top electrode may be formed adjacent to the referencelayer 112. These additional or alterative features are all possible andincluded in the disclosure.

FIG. 1 shows that in the MTJ structure 110, the free layer 116 isstacked below the reference layer 112 for illustrative purposes. Inother embodiment, the free layer 116 is stacked over the reference layer112 and the SOT metal layer 130 is position adjacent to the free layer116 over the reference layer 112.

In the description herein, the read and write lines of the MRAM cellsare illustrated as implemented through Word lines, which is notlimiting. It is also possible, depending on MRAM circuitry design, thatthe read and write lines are implemented through Bit lines.

In another example, a shape anisotropy, e.g., a long axis, of the MTJstructure 110 may be positioned with a canting angle with a flowdirection of the SOT current. FIG. 2 shows a top view of the MTJstructure 110 together with the SOT metal layer 130. As shown in FIG. 2, the MTJ 110 is positioned over the SOT metal layer 130 in a cantingconfiguration. For example, the long axis 210 of the ellipticcylindrical MTJ 110 (or specifically, the free layer 116) has a cantingangle θ1 with respect to the path 220 of the write current 230. Thecanting angle θ1 is used to help the magnetization orientation of thefree layer 116 to engage into a precession process after the SOT currentof the SOT metal layer 130 is removed. The canting angle θ1 is not usedto determinatively settle the magnetization orientation of the freelayer 116 under the SOT effect. As such, the canting angle θ1 does notneed to be large. In an embodiment, the canting angle θ1 may be smallerthan ±5 degree (or larger than ±85 degree) in a range between about 1degree to about 5 degree. Larger canting angles (larger than 5 degree orsmaller than 85 degree) are possible dependent on device or systemdesign requirements. A non-zero canting configuration is preferable toenhance the precession process, although a zero canting angle is alsopossible under the disclosure techniques. Such a small canting angle ismade possible due to the use of the V_(VCMA) 154 in addition to anI_(SOT) 230 in the write operation as described herein. Such a small orzero canting angle θ1 improves power efficiency of a MRAM device havingthe MTJ 110.

FIG. 3 shows an example configuration of switching the MTJ 110 statebetween AP and P. Referring to FIG. 3 , a current source 230 is coupledto provide a SOT current 230 to flow through the SOT metal layer 130.For simplicity purposes, the referral number 230 is used to refer toeither one or both of the SOT current source or the SOT current asapplicable. The V_(VCMA) voltage source 154 is coupled between thereference layer 112 and the free layer 114, through the SOT metal layer130. For simplicity purposes, the referral number 154 is used to referto either one or both of the VCMA voltage source and the VCMA voltage asapplicable. A switching unit 320 is couple to enable one of the I_(SOT)current 230 or the V_(VCMA) 154 to be applied. The switching unit 320 isillustrated as a three-way switch for illustrative purposes, which doesnot limit the scope of the disclosure. The I_(SOT) 230 and the V_(VCMA)154 may be sequentially applied through any switching mechanisms, whichare all included in the disclosure.

The switching unit 320 is controlled by a timing control unit 330. Thetiming control unit 330 may be implemented through hardware logic,embedded software (firmware), a computing device, or other suitableimplementation approaches.

FIG. 4A to 4D shows an example write operation of switching the MTJ 110state from the P state to the AP state. As shown in FIG. 4A, the MTJ 110is initially in a P state in that the magnetization orientations of thereference layer 112 and the free layer 116 are parallel, shown as bothin an up orientation for illustrative purposes. This initial P state mayrepresent a logic state stored in the MRAM cell containing the MTJ 110.At this stage, the write operation has not started and both the SOTcurrent source 230 and the VCMA voltage source 154 are not connected,e.g., both the I_(SOT) 230 and the V_(VCMA) 154 are off.

In FIG. 4B, a P-to-AP write operation starts and the SOT current I_(SOT)230 is firstly (i.e., before the V_(VCMA) 154 is applied) appliedthrough the SOT metal layer 130 in a first direction, shown by thearrow. The SOT current I_(SOT) 230 is on and the VCMA voltage V_(VCMA)154 is off. The I_(SOT) 230 causes a SOT effect that pulls themagnetization orientation of the free layer 116 into an in-planeorientation 410 following the shape anisotropy of the free layer 116,e.g., the long axis of the free layer 116. When the I_(SOT) 230 isapplied, the VCMA voltage source 154 is not applied.

In FIG. 4C, with the write operation continuing, the SOT current sourceI_(SOT) 230 is removed and the VCMA voltage V_(VCMA) 154 is applied tothe MTJ structure 110. The SOT current I_(SOT) 230 is off and the VCMAvoltage V_(VCMA) 154 is on. The V_(VCMA) 154 has a voltage valuesufficiently large to overcome or remove the energy barrier of the Pstate MTJ 110 accumulated on the two sides of the tunnel barrier layer114, which interfaces with the free layer 116 or the reference layer 12,respectively. Without the energy barrier and the SOT effect, themagnetization orientation of the free layer 116 enters into a precessionprocess 420, in which the magnetization orientation rotates around theshape anisotropy of the free layer 116, e.g., the long axis 210 (FIG. 2). The canting angle θ1 (FIG. 2 ) helps to provide a damping torque forthe precession.

As shown by FIGS. 4B and 4C, the I_(SOT) 230 and the V_(VCMA) 154 areapplied sequentially with the V_(VCMA) 154 being subsequent to theI_(SOT) 230. A delay between the application of the I_(SOT) 230 and theapplication of the V_(VCMA) 154 is acceptable as long as V_(VCMA) 154 isapplied before the magnetization orientation of the free layer 116settles at a perpendicular orientation of either the P state or the APstate. To improve system speed, a shorter delay between the I_(SOT) 230and the V_(VCMA) 154 is generally desired.

As shown in FIG. 4D, the V_(VCMA) 154 is removed at a point thatmagnetization orientation of the free layer is adjacent to the targetperpendicular orientation, either P or AP, that is set for the MTJstructure 110 under write operation. For example, the V_(VCMA) 154 isremoved when the magnetization orientation of the free layer 116 is at aprecession end position 430 that is more adjacent to the AP stateorientation, here for example the down orientation, than to the P stateorientation, here the up orientation. In an embodiment, the V_(VCMA) 154is removed when the precession end position 430 is closer to the targetperpendicular orientation than the adjacent in-plane orientation. Assuch, after the precession process ends, the magnetization orientationof the free layer 116 will not temporally go back to the in-planeorientation and settle randomly between the AP or P state from thein-plane orientation.

With the V_(VCMA) 154 removed with a proper timing, the magnetizationorientation of the free layer exits the precession process 420 andsettles at the target perpendicular orientation, here the AP stateorientation, which is adjacent to the precession end position 430.

FIG. 5A to 5D shows an example write operation of switching the MTJ 110state from the AP state to the P state. As shown in FIG. 5A, the MTJ 110is initially in an AP state in that the magnetization orientations ofthe reference layer 112 and the free layer 116 are antiparallel, wherethe magnetization orientation of the reference layer 112 is at an uporientation and the magnetization orientation of the free layer 116 isat a down orientation for illustrative purposes. This initial AP statemay represent a logic state stored in the MRAM cell containing the MTJ110. At this stage, the write operation has not started and both the SOTcurrent source 230 and the VCMA voltage source 154 are not connected tothe MTJ 110, e.g., both the I_(SOT) 230 and the V_(VCMA) 154 are off.

In FIG. 5B, a AP-to-P write operation starts and the I_(SOT) 230 isfirstly applied through the SOT metal layer 130 in a second directionthat is different from the first direction shown in FIG. 4B. The I_(SOT)230 causes a SOT effect that pulls the magnetization orientation ororientation of the free layer 116 into an in-plane orientation 510following the shape anisotropy of the free layer 116, e.g., the longaxis of the free layer 116. When the I_(SOT) 230 is applied, theV_(VCMA) 154 is not applied. That is, the SOT current I_(SOT) 230 is onand the V_(VCMA) 154 is off. As shown here, the SOT current I_(SOT) 230is applied in an second direction opposite to the first direction ofFIG. 4B because the initial perpendicular magnetization orientation ofthe free layer 112 is different from that of FIG. 4A.

In FIG. 5C, with the write operation continuing, the I_(SOT) 230 isremoved and the V_(VCMA) 154 is applied to the MTJ structure 110. TheSOT current I_(SOT) 230 is off and the VCMA voltage V_(VCMA) 154 is on.The V_(VCMA) 154 has a voltage value sufficiently to overcome the energybarrier of the AP state MTJ 110 accumulated on the two sides of thetunnel barrier layer 114 that are adjacent to the free layer 116 or thereference layer 112, respectively. It should be appreciated that theenergy barrier for the AP state of the MTJ 110 may be different from,e.g., higher than, the energy barrier of the P state MTJ 110. As such,the V_(VCMA) 154 may be applied with a different voltage value to besufficient to eliminate the respective energy barrier. Without theenergy barrier and the SOT effect, the magnetization orientation of thefree layer 116 enters into a precession process 520, in which themagnetization orientation rotates around the long axis 210 of the MTJ110 or specifically the free layer 116. The canting angle θ1 (FIG. 2 ),if any, helps to provide a damping torque for the precession process.

As shown by FIGS. 5B and 5C, the I_(SOT) 230 and the V_(VCMA) 154 areapplied sequentially with the V_(VCMA) 154 applied subsequent to theI_(SOT) 230. A delay between the application of the I_(SOT) 230 and theapplication of the V_(VCMA) 154 is acceptable as long as the V_(VCMA)154 is applied before the magnetization orientation of the free layer116 settles at a perpendicular orientation of either P state or APstate. To improve system speed, a shorter delay between the I_(SOT) 230and the V_(VCMA) 154 is generally desired.

As shown by FIGS. 4C and 5C, the voltage source 154 is a DC voltage andalthough the voltage value may change between the P-to-AP switching andthe AP-to-P switching, the direction of the V_(VCMA) 154 stays the samebetween the P to AP switching and the AP to P switching.

As shown in FIG. 5D, the V_(VCMA) 154 is removed at a point thatmagnetization orientation of the free layer is adjacent to the target Pstate perpendicular orientation that is set for the MTJ structure 110under write operation. For example, the V_(VCMA) 154 is removed when themagnetization orientation of the free layer 116 is at a precession endposition 530 that is more adjacent to the P state orientation, here forexample the up orientation, than to the AP state orientation, here thedown orientation. In an embodiment, the V_(VCMA) 154 is removed when theprecession end position 530 is closer to the target P stateperpendicular orientation than the adjacent in-plane orientation. Assuch, after the precession process ends, the magnetization orientationof the free layer 116 will not temporally go back to the in-planeorientation and settle randomly between the AP or P state from thein-plane orientation.

With the V_(VCMA) 154 removed, the magnetization orientation of the freelayer 116 exits the precession process 520 and settles at the P stateperpendicular orientation, which is adjacent to the precession endposition 530 when the V_(VCMA) 154 is removed.

FIGS. 6A-6D show example timing control of the on/off of the I_(SOT) 230and the V_(VCMA) 154 in four example scenarios. In each of the FIGS.6A-6D, a timing chart of the I_(SOT) 230 and the V_(VCMA) 154 isprovided in correspondence to a waveform chart of the magnetization ofthe free layer 116 in one or more of the x-axis, y-axis and the z-axis.FIG. 6A is an example scenario that the MTJ 110 is switched from the Pstate to the AP state under a transient timing control approach, e.g.,with faster switching speed. The faster switching speed is referred towith respect to the steady timing control approach shown in FIG. 6B asdiscussed in details herein.

Referring to FIG. 6A, with reference also to FIGS. 4A-4D, at the timingstate (1), both the SOT current I_(SOT) 230 and the VCMA voltageV_(VCMA) 154 are off, e.g., at the zero level, and the MTJ 110 is at theinitial P state, see FIG. 4A, where the magnetization orientation of thefree layer 116 is perpendicular and is in parallel with that of thereference layer 112. FIG. 6A shows that at the timing state (1), themagnetization of the free layer 116 is at a positive maximum value,positive “1.0”, at the z-axis (“Z-component”), indicating, e.g., thefree layer 116 is at the P state perpendicular orientation with amaximal magnetization value. FIG. 6A also shows that at the timing stage(1), the x-axis magnetization (“X-component”) and the y-axismagnetization (“Y-component”) are all equal to zero, which indicatesthat the magnetization orientation of the free layer 116 is fullyperpendicular. Note that the X-component, Y-component and theZ-component are all defined with respect to the free layer 116 itselffor illustrative purposes.

At the timing state (2), with reference also to FIG. 4B, an I_(SOT) 230of, for example, 0.5 mA, is applied. The I_(SOT) 230 is applied with afirst flow direction, shown as negative (“−”) through the SOT metallayer 130. With the rendered SOT effect, the Z-component value (“mz”)changes from +1.0 (parallel perpendicular orientation) toward 0(in-plane orientation), while one or more of the X-component (“mx”) orthe Y-component (“my”) becomes non-zero as the magnetization of the freelayer 116 is pulled from the perpendicular orientation toward thein-plane orientation. With the I_(SOT) 230 continuously applied, theZ-component will be pulled to the zero and vibrate about the zero linein a transient period before it settles at zero in a steady in-planestate. Specifically, the Z-component will be firstly pulled by theI_(SOT) 230 beyond the zero line to the AP direction (“−”) and then willvibrate back and forth between the P direction (+) and the AP direction(−) about the zero line before it settles at the zero line. Thetransient timing control removes the I_(SOT) 230 during the transientperiod and before the z-component settles at the zero line. For example,the I_(SOT) 230 is removed or turned off when the Z-component is pulledadjacent to the zero line. As shown in FIG. 6A as an example, theI_(SOT) 230 is removed when the Z-component is pulled below thezero-line at the first time. This example does not limit the scope ofthe disclosure and the I_(SOT) 230 may be removed at other time pointswhen the Z-component is pulled adjacent to the zero-line. For example,the I_(SOT) 230 may be removed when the z-component is within a range of±0.1 about the zero line, 0.1 indicates 10% of the magnetization valueat the P or AP states (±1.0, respectively). In an embodiment, theI_(SOT) 230 may be removed when the Z-component is within a range of±0.05 about the zero line. With the I_(SOT) 230 removed, the timingstage (2) terminates.

At the timing state (3), with reference also to FIG. 4C, the V_(VCMA)154 is applied. The V_(VCMA) 154 is applied with a voltage valuesufficient to eliminate the energy barrier of the P state. Here, avoltage value of 1.2V is shown as an illustrative example. The voltageis a DC voltage. With the V_(VCMA) 154 is applied, the magnetization ofthe free layer 116 enters into a precession process, in which theZ-component and one or more of the X-component and the Y componentrotate or vibrate between the +1 and −1 and the intermediate statestherebetween. The V_(VCMA) 154 is removed at a point when themagnetization orientation of the free layer 116 rotates to a positionthat is more adjacent to the target perpendicular orientation, here AP,than the opposite perpendicular orientation P. FIG. 6A shows the P-to-APswitching, where the AP orientation is the target orientation. As such,the V_(VCMA) 154 is removed at a point where the Z-components is in theAP direction, e.g., Z-component value is negative. In an embodiment,V_(VCMA) 154 is removed at a point when the magnetization orientation ofthe free layer 116 rotates to a position that is more adjacent to thetarget perpendicular orientation AP than an adjacent in-planeorientation. For example, as shown in FIG. 6A, the V_(VCMA) 154 isremoved at a point when the Z-component is about −0.625, i.e., themagnetization orientation of the free layer 116 is closer to the APstate (−1) than the adjacent in-plane orientation (0). A range of thepositions where the magnetization orientation of the free layer 116 iscloser to the target perpendicular orientation (P or AP) than theadjacent in-plane orientation (0) is referred to as the target zone. Ifthe V_(VCMA) 154 is removed when the magnetization orientation of thefree layer 116 is within a target zone, here the AP target zone, themagnetization orientation of the free layer 116 tends to settle at thetarget AP perpendicular orientation instead of temporally going back tothe in-plane orientation and then settling randomly at one of the AP orthe P state orientation.

As a transient timing control, FIG. 6A shows that the V_(VCMA) 154 isremoved at the first time the magnetization orientation of the freelayer 116 rotates into the target zone. This is not necessary. Due tothe nature of the precession process, the magnetization orientation ofthe free layer 116 may revisit the target zone until the V_(VCMA) 154 isremoved to end the precession. FIG. 7 shows an example precessionprocess and the target zones to remove the V_(VCMA) 154. As shown inFIG. 7 , with the V_(VCMA) 154 continuously applied, the Z-component(“mz”) waveform 710 may enter the AP target zone 720 (a zone between−0.5 to −1 of the Z-component “mz” precession wave) multiple times. TheZ-component (“mz”) waveform 710 may also enter the P target zone 740 (azone between 0.5 to 1 of the Z-component “mz” precession wave) multipletimes. In a case that the V_(VCMA) 154 is removed when the Z-componentis in the AP target zone 720, the magnetization orientation of the freelayer 116 will end precession and settle at the AP orientation. When theV_(VCMA) 154 is removed, the timing stage (3) terminates.

Referring back to FIG. 6A, with reference also to FIG. 4D, in timingstage (4), with the V_(VCMA) 154 and the I_(SOT) 230 both turned off,the magnetization orientation of the free layer 116 gradually ends theprecession and settles at the target perpendicular orientation, here theAP orientation.

FIG. 6B is an example scenario that the MTJ 110 is switched from the Pstate to the AP state in a steady timing control, e.g., with a slowerswitching speed. The slower switching speed is referred to with respectto the transient timing control shown in FIG. 6A as discussed in detailsherein.

Referring to FIG. 6B, with reference also to FIGS. 4A-4D, the timingstage (1) and the timing stage (4) in FIG. 6B are similar to those ofFIG. 6A. For simplicity purposes, the description of the timing stages(1) and (4) of FIG. 6B are omitted. Referring to timing stage (2) ofFIG. 6B, under the steady timing control, the I_(SOT) 230 is not removedwhen the Z-component “mz” is firstly pulled to a position adjacent thezero line. That is, the I_(SOT) 230 is not removed when themagnetization orientation of the free layer 116 is pulled transientlyin-plane and is still vibrating. Instead, the I_(SOT) 230 is removedwhen the magnetization orientation of the free layer 116 become steadyat the in-plane orientation. As illustratively shown in FIG. 6B, themagnetization orientation of the free layer 116 is pulled by theadjacent to the in-plane orientation at about 0.7 ns while the I_(SOT)230 is removed at about 2 ns after the application of the I_(SOT) 230.

Referring to the timing stage (3) of FIG. 6B, because the V_(VCMA) 154is applied when the magnetization orientation of the free layer 116becomes steadily at the in-plane orientation, it may take a longerperiod of precession time for the magnetization orientation of the freelayer 116 to enter the target zone, here the AP target zone 720 (FIG. 7). FIG. 6B shows that it takes about 2 ns for the magnetizationorientation of the free layer 116 to enter the AP target zone 720 at thefirst time. For comparison, in FIG. 6A, it takes about 1 ns for themagnetization orientation of the free layer 116 to enter the AP targetzone 720 at the first time. So the steady timing control tends toprolong or delay the timing stage (3) as well as the timing stage (2).

The steady timing control or the transient timing control both have itsown advantages. For example, the steady timing control provides moretolerance and flexibility in the timing design of the system. Thetransient timing control provides much faster speed in switching betweenthe P state and the AP state of the MTJ 110.

FIG. 6C is an example scenario that the MTJ 110 is switched from the APstate to the P state in a transient timing control, e.g., fasterswitching speed. The faster switching speed is referred to with respectto the steady timing control shown in FIG. 6D as discussed in detailsherein.

Referring to FIG. 6C, with reference also to FIGS. 5A-5D, at the timingstate (1), both the I_(SOT) 230 and the V_(VCMA) 154 are off, e.g., atthe zero level, and the MTJ 110 is at the initial AP state, see FIG. 5A,where the magnetization orientation of the free layer 116 isperpendicular and is anti-parallel with that of the reference layer 112.FIG. 6A shows that at the timing state (1), the magnetizationorientation of the free layer 116 is at a negative maximum value,“−1.0”, indicating an AP perpendicular orientation with maximalmagnetization value in the z-axis. FIG. 6C also shows that at the timingstage (1), the X-component (“mx”) and the Y-component (“my”) are allequal to zero, which indicates that the magnetization orientation of thefree layer 116 is fully perpendicular.

At the timing state (2), with reference also to FIG. 5B, an I_(SOT) 230of 0.5 mA is applied. The I_(SOT) 230 is applied with a second flowdirection, shown as positive (“+”), through the SOT metal layer 130.Note that the I_(SOT) 230 for the AP-to-P switch has a different flowdirection than that of the P-to-AP switch as shown in FIGS. 6A and 6B.With the SOT effect rendered, the Z-component value changes from −1.0(anti-parallel perpendicular orientation) toward 0 (in-planeorientation), while one or more of the X-component or the Y-componentvalue becomes non-zero because the magnetization orientation of the freelayer 116 is pulled from the perpendicular orientation toward thein-plane orientation. With the I_(SOT) 230 continuously applied, theZ-component will be pulled to the zero and vibrate about the zero in atransient period before it settle at zero in a steady in-planeorientation. In the transient period, the Z-component will be firstlypulled by the I_(SOT) 230 beyond the zero to the P direction and thenvibrates back and forth between the P direction (+) and the AP direction(−) about the zero line before it settles at the zero line. Thetransient timing control approach eliminates or reduces the vibration byremoving the I_(SOT) 230 during the transient period. For example, theI_(SOT) 230 is removed or turned off immediately upon the Z-component isfirstly pulled adjacent to the zero line. As shown in FIG. 6C as anexample, the I_(SOT) 230 is removed when the Z-component is firstlypulled above the zero-line before the Z-component vibrates back to theAP orientation. This example does not limit the scope of the disclosureand the I_(SOT) 230 may be removed at other time points in the transientperiod. For example, the I_(SOT) 230 may be removed when the z-componentis within a range of ±0.1 about the zero line, where 0.1 indicating 10%of the magnetization value at the P or AP states (±1.0, respectively).In an embodiment, the I_(SOT) 230 may be removed when the z-component iswithin a range of ±0.05 about the zero line. With the I_(SOT) 230removed, the timing stage (2) terminates.

At the timing state (3), with reference also to FIG. 5C, the V_(VCMA)154 is applied. The V_(VCMA) 154 is applied with a voltage valuesufficient to eliminate the energy barrier of the AP state. Here, avoltage value of 1.2V is shown as an illustrative example, same as theP-to-AP switch of FIGS. 6A, 6B. However, the voltage value for theAP-to-P switch may be different from, e.g., larger than, that of theP-to-AP switch because the energy barrier accumulated on the two sidesof the tunnel barrier layer 114 may be different. The V_(VCMA) 154 is aDC voltage. That is, a same voltage direction is applied for the AP-to-Pswitch and the P-to-AP switch. With the V_(VCMA) 154 applied, themagnetization orientation of the free layer 116 enters a precessionprocess, in which the Z-component and one or more of the X-component andthe Y component rotate or vibrate between the polarities +1 and −1 andthe intermediate states therebetween. The V_(VCMA) 154 is removed at apoint when the magnetization orientation of the free layer 116 rotatesto a position that is more adjacent to the target perpendicularorientation, e.g., the P state orientation, than the oppositeperpendicular orientation, the AP state orientation. FIG. 6C shows theAP-to-P switching, where the P orientation is the target orientation. Assuch, the V_(VCMA) 154 is removed at a point where the Z-component is inthe P direction, e.g., Z-component value is positive in FIG. 6C. In anembodiment, V_(VCMA) 154 is removed at a point when the magnetizationorientation of the free layer 116 rotates to a position that is moreadjacent to the target P state orientation than an adjacent in-planeorientation. For example, as shown in FIG. 6C, the V_(VCMA) 154 isremoved at a point when the Z-component is about +0.625, i.e., themagnetization orientation of the free layer 116 is closer to the P state(+1 for Z-component) than the adjacent in-plane orientation (0 forZ-component). A range of the positions where the magnetizationorientation of the free layer 116 is closer to the target perpendicularorientation (+1) than the adjacent in-plane orientation (0) is referredto as the target zone. If the V_(VCMA) 154 is removed when themagnetization orientation of the free layer 116 is within the targetzone, the magnetization orientation of the free layer 116 tends tosettle at the target P state perpendicular orientation instead oftemporally going back to the adjacent in-plane orientation and thensettling randomly at one of the AP or the P state orientation.

As a transient timing control, FIG. 6C shows that the V_(VCMA) 154 isremoved at the first time the magnetization orientation of the freelayer 116 rotates into the P state target zone. This is not necessary.Due to the nature of the precession process, the magnetizationorientation of the free layer 116 may revisit the target zone until theV_(VCMA) 154 is removed.

FIG. 8 shows an example precession process 800 with AP state target zone820 and P state target zone 840. As shown in FIG. 8 , with the V_(VCMA)154 continuously applied, the Z-component (“mz”) waveform 810 may enterthe AP target zone 820 (a zone between −0.5 to −1 of the mz precession810 waveform) and the P target zone 840 (a zone between +0.5 to +1 ofthe mz precession 810 wave) multiple times. In a case that the V_(VCMA)154 is removed when the Z-component is in the P target zone 840, themagnetization orientation of the free layer 116 will end precession andsettle at the P state perpendicular orientation. When the V_(VCMA) 154is removed, the timing stage (3) terminates.

In FIGS. 7 and 8 , the z-component waveforms of the magnetization areshown as vibrating between −1 and 1 in the precession process. This isan example scenario where the magnetization orientation can temporarilyreaches the perpendicular P state or the AP state orientations in theprecession. In the case that the magnetization of the free layer 116includes one or more of the X-component or the Y-component, themagnetization may not rotate to the full AP or P state orientation andthe Z-component may not vibrate between values −1 and 1 (i.e., the fullmagnetization value). Instead, the Z-component mz will be smaller thanthe full magnetization value 1. All such variant scenarios are possibleand included in the disclosure.

Referring back to FIG. 6C, with reference also to FIG. 5D, in timingstage (4), with the V_(VCMA) 154 and the I_(SOT) 230 are both turnedoff, the magnetization orientation of the free layer 116 gradually endsthe precession and settles at the target perpendicular orientation, herethe P orientation.

FIG. 6D is an example scenario that the MTJ 110 is switched from the APstate to the P state in a steady timing control, e.g., with a slowerswitching speed. The slower switching speed is referred to with respectto the transient timing control shown in FIG. 6C as discussed in detailsherein.

Referring to FIG. 6D, with reference also to FIGS. 5A-5D, the timingstage (1) and timing stage (4) in FIG. 6D are similar to that of FIG.6C. For simplicity purposes, the description of the timing stages (1)and (4) of FIG. 6D are omitted. Referring to timing stage (2) of FIG.6D, for the steady timing control, the I_(SOT) 230 is not removed untilthe magnetization orientation of the free layer 116 becomes steady atthe in-plane orientation. As illustratively shown in FIG. 6D, themagnetization orientation of the free layer 116 is pulled by the I_(SOT)230 transiently adjacent to the in-plane orientation at about 0.7 nswhile the I_(SOT) 230 is removed at about 2 ns after its application.

Referring to timing stage (3) of FIG. 6B, because the V_(VCMA) 154 isapplied when the magnetization orientation of the free layer 116 becomessteadily at the in-plane orientation, it may take longer period ofprecession time for the magnetization orientation of the free layer 116to enter the target zone, here the P state target zone (see also, Pstate target zone 840 in FIG. 8 ). FIG. 6D shows that it takes about 4ns for the magnetization of the free layer 116 to enter the AP targetzone, e.g., between 0.5 to 1, at the first time. In FIG. 6C, it takesabout 1 ns for the magnetization orientation of the free layer 116 toenter the P target zone. So the steady timing control tends to prolongor delay the timing stage (3) as well as the timing stage (2). As shownin FIG. 6D, the magnetization orientation of the free layer 116 firstrotate toward the AP state orientation before it moves toward the Pstate orientation, which is an illustrative example and does not limitthe scope of the disclosure.

The effects of the on/off effects of the I_(SOT) 230 or the V_(VCMA) 154may be determined based on one or more of simulation or experiments. Forexample, the waveforms of the FIGS. 6A-6D and 7 and 8 may be obtainedthrough simulation or experiments. With those waveforms provided, thetiming control of the timing stages (1), (2), (3), (4) of the FIGS.6A-6D can be determined accordingly, depending on circuit and devicesdesigns and configurations. In further embodiments, alternatively oradditionally, the magnetization orientation of the free layer 116, e.g.,the magnetization orientation or the magnetization values in one or moreof the X-component, Y-component or the Z-component, may be monitored ormeasured in real time and the real-time monitoring results may be usedto control the timing of the I_(SOT) 230 or the V_(VCMA) 154.

FIG. 9 shows an example process 900. Referring to FIG. 9 , in exampleoperation 910, an initial logic state of a MRAM memory cell 100 isidentified. The logic state corresponds to the state of the MTJstructure 110 of the MRAM cell, i.e., either AP or P.

In example operation 920, a first part of a write operation is conductedby applying an I_(SOT) 230 onto the MRAM cell 100, e.g., through a SOTmetal layer 130. The I_(SOT) 230 is applied for with a flow directiondetermined based on the initial logic state of the MRAM cell 100 and fora first duration that is sufficiently long to at least pull themagnetization orientation of the free layer 116 of the MTJ structure 110adjacent to the in-plane orientation.

In example operation 930, a second part of the write operation isconducted by applying a V_(VCMA) 154 onto the MRAM cell 100, after theI_(SOT) 230 is removed. The V_(VCMA) 154 has a voltage value that issufficiently large to remove the energy barrier accumulated on bothsides of the tunnel barrier layer 114 of the MTJ structure 110, whilethe V_(VCMA) 154 is not so large as to break the dielectric barrier ofthe tunnel barrier layer 114. The V_(VCMA) 154 enables the magnetizationorientation of the free layer 116 to enter into a precession process.The V_(VCMA) 154 is removed when the magnetization orientation of thefree layer 116 rotates to a position within a target zone of the targetmagnetization state under the write operation, i.e., either P or AP. Itshould be appreciated that the target state of the MTJ 110 may be thesame as the initial state or may be a difference one of AP or P.

With the voltage-controlled magnetic anisotropy effect rendered by theV_(VCMA) 154, the disclosed techniques achieve a deterministic switchingof SOT-MTJ without the assistance of an external field or a largecanting angle. A small canting angle of less than 5 degree is desirablebut not required. With such a small canting angle, power consumption andswitching speed can both be improved comparing to traditional SOT-MTJ.

The present disclosure may be further appreciated with the descriptionof the following embodiments:

In a method embodiment, a first heavy metal layer is formed over asubstrate. A dielectric material is deposited over the first heavy metallayer. An average thickness of the deposited dielectric material iscontrolled to be less than a diameter of a molecule of the dielectricmaterial. A second heavy metal layer is formed over the dielectricmaterial and the first heavy metal layer.

In another embodiment, a structure includes a magnetic tunnel junctionstructure including a reference layer, a free layer and a tunnelingbarrier layer sandwiched between the reference layer and the free layer.A spin-orbit torque layer is positioned adjacent to the free layer ofthe magnetic tunnel junction structure. The spin-orbit torque layerincludes a first heavy metal layer, a second heavy metal layer and afirst dielectric layer sandwiched between the first heavy metal layerand the second heavy metal layer.

In a further embodiment, a memory device includes a substrate, atransistor over the substrate, and a magnetoresistive random accessmemory cell over the transistor. The transistor has a first source/drainterminal, a second source/drain terminal and a gate terminal. Themagnetoresistive random access memory cell includes a magnetic tunneljunction structure and a spin-orbit torque structure adjacent to themagnetic tunnel junction structure. A write signal line is coupled tothe gate terminal of the transistor. A first current node is coupled tothe first source/drain terminal. A first end of the spin-orbit torquestructure is coupled to the second source/drain terminal. A second endof the spin-orbit torque structure is coupled to a second current node.The spin-orbit torque structure includes a first heavy metal layer, asecond heavy metal layer stacked over the first heavy metal layer, and afirst plurality of molecules of a dielectric material scattered adjacentto an interface between the first heavy metal layer and the second heavymetal layer.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A device, comprising: a magnetic tunnel junctionstructure including a reference layer, a free layer and a tunnelingbarrier layer stacked vertically between the reference layer and thefree layer; a spin-orbit torque metal layer adjacent to the free layerof the magnetic tunnel junction structure; a current source coupled tothe spin-orbit torque metal layer and configured to apply a currentthrough the spin-orbit torque metal layer in one of two oppositedirections; a voltage source coupled to the magnetic tunnel junctionstructure and configured to apply an electrical potential on two sidesof the tunneling barrier layer that interface with the reference layeror the free layer, respectively; and a control element configured tocontrol through a switch that the electrical potential is applied on thetwo sides of the tunneling barrier layer after the current through thespin-orbit torque metal layer is removed in a write operation of themagnetic tunnel junction structure.
 2. The device of claim 1, whereinthe voltage source is coupled between the reference layer and thespin-orbit torque metal layer.
 3. The device of claim 1, wherein thevoltage source is a direct current voltage source.
 4. The device ofclaim 1, further comprising a switching element configured to apply thecurrent source or the voltage source sequentially in a write operation,with the current source being applied before the voltage source.
 5. Thedevice of claim 2, wherein the control element is configured to controlone or more of a first timing of turning off the current source or asecond timing of turning off the voltage source.
 6. A device,comprising: a magnetic tunnel junction structure, the magnetic tunneljunction structure including a reference layer, a free layer and atunneling barrier layer stacked between the reference layer and the freelayer, two sides of the tunneling barrier layer interfacing with thereference layer or the free layer, respectively; a spin-orbit torquemetal layer adjacent to the free layer of the magnetic tunnel junctionstructure; and control circuitry electrically coupled to the magnetictunnel junction structure and the spin-orbit torque metal layer, thecontrol circuitry configured to control a write operation of themagnetic tunnel junction structure through one or more switch elementsto: apply a spin-orbit torque current through the spin-orbit torquemetal layer during a first time period; and apply a voltage between thetwo sides of the tunneling barrier layer during a second time periodsubsequent to the first time period and after the spin-orbit torquecurrent has been removed, the voltage being smaller than a firstthreshold such that the tunneling barrier layer remains electricalinsulating during the second time period.
 7. The device of claim 6,wherein the control circuitry includes: a current source coupled to twoends of the spin-orbit torque metal layer; a voltage source coupled tothe free layer and the reference layer; and a control element coupled tocontrol the current source and the voltage source.
 8. The device ofclaim 6, wherein the control circuitry is configured to identify amagnetization orientation of the free layer is in one of a firstperpendicular orientation or a second perpendicular orientation beforethe first time period.
 9. The device of claim 8, wherein the controlcircuitry is configured to apply the spin-orbit torque current to flowthrough the spin-orbit torque metal layer in a direction selected basedon the magnetization orientation of the free layer before the first timeperiod.
 10. The device of claim 8, wherein the control circuitry isconfigured to apply the spin-orbit torque current to flow through thespin-orbit torque metal layer in a same direction no matter whether themagnetization orientation of the free layer is in the firstperpendicular orientation or in the second perpendicular orientationbefore the first time period.
 11. The device of claim 6, wherein thecontrol circuitry is configured to remove the spin-orbit torque currentin response to detecting that a magnetization of the free layer ispulled from a first perpendicular orientation to a second orientationadjacent to an in-plane orientation.
 12. The device of claim 11, whereinthe control circuitry is configured to remove the spin-orbit torquecurrent before the detected second orientation of the magnetization ofthe free layer stabilizes at the in-plane orientation.
 13. The device ofclaim 11, wherein the control circuitry is configured to remove thespin-orbit torque current after the detected second orientation of themagnetization of the free layer stabilizes at the in-plane orientation.14. The device of claim 6, wherein the control circuitry is configuredto remove the voltage in response to a magnetization orientation of thefree layer is detected to rotate in a precession process to a positionthat is more adjacent to a first perpendicular orientation that is setfor the magnetic tunnel junction structure than a second perpendicularorientation opposite to the first perpendicular orientation.
 15. Thedevice of claim 14, wherein the control circuitry is configured toremove the voltage in response to the magnetization orientation of thefree layer is detected to rotate to a position that is more adjacent tothe first perpendicular orientation that is set for the magnetic tunneljunction structure than an adjacent in-plane orientation.
 16. The deviceof claim 6, wherein the control circuitry is configured to apply thespin-orbit torque current to flow in a direction that has a cantingangle with a shape anisotropy of the free layer, the canting angle beingone of smaller than 5 degree or larger than 85 degree.
 17. The device ofclaim 6, wherein the control circuitry is configured to apply thespin-orbit torque current to flow in a direction that has a cantingangle with a shape anisotropy of the free layer, the canting angle beingwithin a range of one of between about 0 degree and about 90 degree orbetween about 90 degree to about 180 degree.
 18. The device of claim 6,wherein the voltage is larger than a second threshold to remove anenergy barrier accumulated on the two sides of the tunneling barrierlayer.
 19. A device, comprising: a magnetoresistive random-access memoryelement, the magnetoresistive random-access memory element having amagnetic tunnel junction structure including a reference layer, a freelayer and a tunneling barrier layer stacked vertically between thereference layer and the free layer; a spin-orbit torque metal layeradjacent to the free layer of the magnetic tunnel junction structure acurrent source coupled to the spin-orbit torque metal layer; a voltagesource coupled to the reference layer and the spin-orbit torque metallayer; and a control element coupled to the current source and thevoltage source, wherein in a write operation of the magnetoresistiverandom-access memory element: the control element controls the currentsource to apply a spin-orbit torque current through the spin-orbittorque metal layer by turning on the current source; the control elementcontrols the current source to remove the spin-orbit torque currentafter a magnetization orientation of the free layer is adjacent to anin-plane orientation; the control element controls the voltage source toapply an electrical potential on the tunneling barrier layer by turningon the voltage source after the removing the spin-orbit torque current,the electrical potential enabling the magnetization orientation of thefree layer engaging into a precession process; and the control elementcontrols the voltage source to remove the electrical potential when themagnetization orientation of the free layer is adjacent to a targetperpendicular orientation in the precession process.
 20. The device ofclaim 19, wherein when the electrical potential is applied, there is noelectrical current flowing through the tunneling barrier layer.